Power transmission apparatus

ABSTRACT

A power transmission apparatus a centrifugal clutch including a holder and a press. The holder and the press are each circumferentially provided with protrusions fitted and attached to cut-outs of a clutch housing. The holder is an integrated assembly into which a mass that is being held is integrated. The integrated assembly and the press are non-connected separate components and are independently movable toward or away from each other.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a power transmission apparatus that isable to freely transmit a rotational force of an input to an output orcut off the rotational force.

2. Description of the Related Art

Usually, a power transmission apparatus included in a motorcycle freelytransmits a driving force of an engine to a transmission and a drivingwheel or cuts off the driving force. Such a power transmission apparatusincludes an input connected to an engine, an output connected to atransmission and a driving wheel, a clutch member connected to theoutput, and a pressure member that is able to move close to or away fromthe clutch member. Bringing the pressure member close to the clutchmember presses driving and driven clutch plates against each other so asto transmit power therebetween. Bringing the pressure member away fromthe clutch member releases a pressing force exerted on the driving anddriven clutch plates so as to cut off transmission of the powertherebetween.

As disclosed, for example, in WO 2013/183588, a power transmissionapparatus known in the art includes a centrifugal clutch means includinga weight member that moves from a radially inner position of a groove toa radially outer position thereof with centrifugal force produced byrotation of a clutch housing and is thus able to press driving anddriven clutch plates against each other. The power transmissionapparatus known in the art is able to apply centrifugal force to theweight member in accordance with the rotation of the clutch housingcaused by driving of an engine and is thus able to press the driving anddriven clutch plates against each other so as to transmit a drivingforce of the engine to a wheel.

SUMMARY OF THE INVENTION

Unfortunately, the centrifugal clutch means of the power transmissionapparatus known in the art holds the weight member in spherical shape(i.e., a spherical member) such that the weight member is movable alonga groove defined in the clutch housing, which disadvantageously not onlyrequires a space for movement of the weight member that is relativelylarge, resulting in an increase in the size of the apparatus, but alsomakes it impossible to place the centrifugal clutch at a differentlocation inside the clutch housing.

The applicant of this application thus has conducted studies on acentrifugal clutch which includes a holder holding a mass and a press topress driving and driven clutch plates against each other in response tomovement of the mass and in which the holder and the press each areprovided with a plurality of circumferentially positioned protrusionsfitted and attached to a fitting portion of a clutch housing. Such acentrifugal clutch is placeable at any location where the fittingportion of the clutch housing is defined.

When the holder, the mass, and the press are separate components,however, the mass, in particular, is prone to fall off, which presumablyconsiderably reduces workability during assembly. When the press isconnected to the holder so as to be movable in an axial direction,asynchronous radial movement of more than one mass may incline the pressrelative to the axial direction and cause the press to be caught by aconnector, which may restrict further movement of the press. The pressthus caught in its track may be brought to a halt and may fail tosuccessfully press the driving and driven clutch plates against eachother.

Preferred embodiments of the present invention provide powertransmission apparatuses that each include a centrifugal clutchplaceable at any location where a fitting portion of a clutch housing isdefined, contributes to improved workability during assembly of thecentrifugal clutch, and enables successful movement of a pressresponsive to movement of a mass.

A power transmission apparatus according to a preferred embodiment ofthe present invention includes a clutch housing that rotates togetherwith an input that rotates due to a driving force of an engine of avehicle, the clutch housing including a fitting portion having aplurality of driving clutch plates fitted and attached thereto, a clutchhaving a plurality of driven clutch plates attached thereto, the drivenclutch plates being alternately arranged with the driving clutch platesattached to the clutch housing, the clutch being connected to an outputthat is able to rotate a wheel of the vehicle, a pressure applicatormovable between an operating position where the driving and drivenclutch plates are pressed against each other so as to enabletransmission of the driving force of the engine to the wheel and anon-operating position where a pressing force exerted on the driving anddriven clutch plates is released so as to cut off transmission of thedriving force of the engine to the wheel, and a centrifugal clutchincluding a mass movable from a radially inner position to a radiallyouter position with centrifugal force produced due to rotation of theclutch housing, the centrifugal clutch being configured to, when themass is located at the radially outer position, press the driving anddriven clutch plates against each other so as to enable transmission ofthe driving force of the engine to the wheel and configured to, when themass is located at the radially inner position, release the pressingforce exerted on the driving and driven clutch plates so as to cut offtransmission of the driving force of the engine to the wheel. Thecentrifugal clutch includes a holder holding the mass such that the massis movable between the radially inner position and the radially outerposition, and a press to press the driving and driven clutch platesagainst each other by moving in a stacking direction of the driving anddriven clutch plates in response to movement of the mass from theradially inner position to the radially outer position. The holder andthe press are each circumferentially provided with a plurality ofprotrusions fitted and attached to the fitting portion of the clutchhousing. The holder is an integrated assembly into which the mass thatis being held is integrated. The integrated assembly and the press arenon-connected separate components and are independently movable towardor away from each other.

The holder may be provided with a housing portion housing the mass. Theholder including a support secured thereto defines the integratedassembly, the support being able to hold the mass so as to preventdisconnection of the mass.

The holder may be provided with a pushing surface located radiallyinward of a housing portion housing the mass. When the holder and thepress move away from each other in response to movement of the mass tothe radially outer position, a pushing surface of the press is able topress the driving and driven clutch plates against each other, and thepushing surface of the holder is able to push an auxiliary clutch platesmaller in diameter than the driving and driven clutch plates.

A first surface of the holder may be provided with the housing portion,and a second surface of the holder is provided with the pushing surface.The pushing surface may be defined by a bottom of a recess in the secondsurface.

According to a preferred embodiment of the present invention, the holderand the press are each provided with the plurality of protrusions fittedand attached to the fitting portion of the clutch housing. The holderdefines the integrated assembly into which the mass that is being heldis integrated. The integrated assembly and the press are non-connectedseparate components and are independently movable toward or away fromeach other. Consequently, this preferred embodiment is able to place thecentrifugal clutch at any location where the fitting portion of theclutch housing is defined, improve workability during assembly of thecentrifugal clutch, and successfully move the press in response tomovement of the mass.

According to another preferred embodiment of the present invention, theholder is provided with the housing portion housing the mass. The holderincluding the support secured thereto defines the integrated assembly.The support is able to hold the mass so as to prevent disconnection ofthe mass. Consequently, this preferred embodiment is able to reliablyprevent the mass from falling off during assembly of the centrifugalclutch.

According to yet another preferred embodiment of the present invention,the holder is provided with the pushing surface located radially inwardof the housing portion housing the mass. When the holder and the pressmove away from each other in response to movement of the mass to theradially outer position, the pushing surface of the press is able topress the driving and driven clutch plates against each other, and thepushing surface of the holder is able to push the auxiliary clutch platesmaller in diameter than the driving and driven clutch plates.Consequently, with the centrifugal clutch, this preferred embodiment isable to press the driving and driven clutch plates against each otherand push the auxiliary clutch plate simultaneously.

According to a further preferred embodiment of the present invention,the first surface of the holder is provided with the housing portion,and the second surface of the holder is provided with the pushingsurface. The pushing surface is defined by the bottom of the recess inthe second surface. Consequently, this preferred embodiment enables theauxiliary clutch plate to fit within a depth dimension of the recess soas to reduce the axial dimension of the apparatus, resulting in areduction in the size of the apparatus.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external view of a power transmission apparatus accordingto a preferred embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1 .

FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 1.

FIG. 4 is a perspective view of a clutch housing of the powertransmission apparatus.

FIG. 5 is a three-view drawing of a first clutch member of the powertransmission apparatus.

FIG. 6 is a perspective view of the first clutch member.

FIG. 7 is a three-view drawing of a second clutch member of the powertransmission apparatus.

FIG. 8 is a perspective view of the second clutch member.

FIG. 9 is a three-view drawing of a pressure member of the powertransmission apparatus.

FIG. 10 is a perspective view of the pressure member.

FIG. 11 is a longitudinal cross-sectional view of a centrifugal clutchof the power transmission apparatus.

FIG. 12 is a partially cutaway perspective view of the centrifugalclutch.

FIG. 13 is a three-view drawing of a holding member included in thecentrifugal clutch.

FIG. 14 is a three-view drawing of a supporting member included in thecentrifugal clutch.

FIG. 15 is a three-view drawing of a pressing member included in thecentrifugal clutch.

FIG. 16 is a four-view drawing of a weight member included in thecentrifugal clutch.

FIG. 17 is a cross-sectional view taken along the line XVII-XVII in FIG.16 .

FIG. 18 is a plan view illustrating a state of the centrifugal clutchwhere each weight member is located at a radially inner position.

FIG. 19 is a plan view illustrating a state of the centrifugal clutchwhere each weight member is located at a radially outer position.

FIG. 20A is a schematic diagram describing how a pressing assist cam ofthe power transmission apparatus acts.

FIG. 20B is a schematic diagram describing how a back torque limiter camof the power transmission apparatus acts.

FIG. 21 is a schematic diagram of a vehicle in which the powertransmission apparatus is used.

FIG. 22 is a cross-sectional view illustrating a state of the powertransmission apparatus where each weight member is located at theradially inner position.

FIG. 23 is a cross-sectional view illustrating a state of the powertransmission apparatus where each weight member is located at anintermediate position between the radially inner position and theradially outer position.

FIG. 24 is a cross-sectional view illustrating a state of the powertransmission apparatus where each weight member is located at theradially outer position.

FIG. 25 is a cross-sectional view illustrating a state of the powertransmission apparatus where each weight member is located at theradially outer position and the pressure member is located at anon-operating position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described belowin detail with reference to the drawings. As illustrated in FIG. 21 , apower transmission apparatus K according to the present preferredembodiment is disposed in a vehicle so as to freely transmit a drivingforce of an engine E to a driving wheel T through a transmission M orcut off the driving force. As illustrated in FIGS. 1 to 17 , the powertransmission apparatus K includes a clutch housing 2 provided with aninput gear 1 (which is an input) that rotates with the driving force ofthe engine E of the vehicle, an output shaft 3 (which is an output)connected to the transmission M, a clutch (which includes a first clutchmember 4 a and a second clutch member 4 b), a pressure member 5 (whichis a pressure applicator), a plurality of driving clutch plates 6, aplurality of driven clutch plates 7, a centrifugal clutch 9 includingweight members 10 (which are masses); and an auxiliary clutch plate 17.

The input gear 1 is rotatable around the output shaft 3 upon receiving adriving force (or a rotational force) transmitted from the engine E. Theinput gear 1 is connected to the clutch housing 2 with a fastener, suchas a rivet. The clutch housing 2 is a cylindrical member with an openingdefined at its right end in FIGS. 2 and 3 and is connected to the inputgear 1. The clutch housing 2 is rotatable together with rotation of theinput gear 1 with the driving force of the engine E.

As illustrated in FIG. 4 , the clutch housing 2 is circumferentiallyprovided with a plurality of cut-outs 2 a. The driving clutch plates 6are fitted to the cut-outs 2A and thus attached to the clutch housing 2.The driving clutch plates 6 are each made of a substantially annularplate material. The driving clutch plates 6 are rotatable together withrotation of the clutch housing 2. The driving clutch plates 6 areslidable in an axial direction (which corresponds to a right-leftdirection in FIGS. 2 and 3 ).

The driven clutch plates 7 are attached to the clutch (which includesthe first clutch member 4 a and the second clutch member 4 b). Thedriven clutch plates 7 are arranged alternately with the driving clutchplates 6 attached to the clutch housing 2. The clutch is connected tothe output shaft 3 (i.e., the output) that is able to rotate the drivingwheel T through the transmission M of the vehicle. The clutch isprovided by assembling two members, i.e., the first clutch member 4 aand the second clutch member 4 b, to each other.

The output shaft 3 is inserted through an insertion hole (see FIGS. 5and 6 ) defined in the center of the first clutch member 4 a. A gearprovided on the first clutch member 4 a and a gear provided on theoutput shaft 3 are in mesh with each other so as to be connected to eachother in the direction of rotation. As illustrated in FIGS. 5 and 6 ,the first clutch member 4 a is provided with inclined surfaces 4 aa eachdefining a pressing assist cam; and inclined surfaces 4 ab each defininga back torque limiter cam. The reference signs “4 ac” in FIGS. 5 and 6each indicate a boss provided with an insertion hole for a bolt B forconnection between the first clutch member 4 a and a securing member 8.

As illustrated in FIGS. 7 and 8 , the second clutch member 4 b is anannular member provided with a flange 4 bb. The driven clutch plates 7are spline-fitted to a spline-fitting portion 4 ba provided on the outerperipheral surface of the second clutch member 4 b and are thus attachedto the second clutch member 4 b. As illustrated in FIGS. 2 and 3 , thepressure member 5 is assembled to the clutch member (which includes thefirst clutch member 4 a and the second clutch member 4 b) such that thedriving and driven clutch plates 6 and 7 are alternately stacked andsecured between a flange 5 c of the pressure member 5 and the flange 4bb of the second clutch member 4 b.

As illustrated in FIGS. 9 and 10 , the pressure member 5 is a diskmember provided with the flange 5 c extending along the peripheral edgeof the pressure member 5. The pressure member 5 is movable between anoperating position where the driving and driven clutch plates 6 and 7are pressed against each other so as to enable transmission of thedriving force of the engine E to the wheel, and a non-operating positionwhere a pressing force exerted on the driving and driven clutch plates 6and 7 is released so as to cut off transmission of the driving force ofthe engine E to the wheel.

More specifically, as illustrated in FIGS. 7 and 8 , the spline-fittingportion 4 ba provided on the second clutch member 4 b defines integralprojections and depressions along substantially the entire outerperipheral side surface of the second clutch member 4 b. Fitting thedriven clutch plates 7 to recessed grooves that define thespline-fitting portion 4 ba restricts movement of the driven clutchplates 7 in the direction of rotation while allowing movement of thedriven clutch plates 7 in the axial direction relative to the secondclutch member 4 b. The driven clutch plates 7 are rotatable togetherwith the second clutch member 4 b.

The driven clutch plates 7 are stacked alternately with the drivingclutch plates 6, making it possible to allow the clutch plates 6 and 7adjacent to each other to be pressed against each other or release thepressing force exerted thereon. In other words, the clutch plates 6 and7 are allowed to slide in the axial direction of the second clutchmember 4 b. Engaging a clutch by pressing the clutch plates (6 a, 6 b, 7a, 7 b) against each other enables a rotational force of the clutchhousing 2 to be transmitted to the output shaft 3 through the secondclutch member 4 b and the first clutch member 4 a. Disengaging theclutch by releasing the pressing force exerted on the clutch plates (6a, 6 b, 7 a, 7 b) causes the first clutch member 4 a and the secondclutch member 4 b to stop following the rotation of the clutch housing 2such that no rotational force will be transmitted to the output shaft 3.

Accordingly, a state where the driving and driven clutch plates 6 and 7are pressed against each other enables transmission of a rotationalforce (i.e., the driving force of the engine E), which is received bythe clutch housing 2, to the driving wheel (or the transmission M)through the output shaft 3 (i.e., the output), and a state where thedriving and driven clutch plates 6 and 7 are not pressed against eachother makes it possible to cut off transmission of the rotational force(or the driving force of the engine E), which is received by the clutchhousing 2, to the output shaft 3 (i.e., the output).

As illustrated in FIGS. 9 and 10 , the pressure member 5 iscircumferentially provided with a plurality of fitting holes 5 d (i.e.,three fitting holes 5 d in the present preferred embodiment). A clutchspring S is fitted into each of the fitting holes 5 d. As illustrated inFIG. 2 , one end of each clutch spring S housed in the associatedfitting hole 5 d is in abutment with the securing member 8, such thateach clutch spring S urges the pressure member 5 in a direction in whichthe driving and driven clutch plates 6 and 7 are to be pressed againsteach other. Operating a clutch actuator (not illustrated) makes itpossible to press the driving and driven clutch plates 6 and 7 againsteach other or stop pressing the driving and driven clutch plates 6 and 7against each other.

In the present preferred embodiment, as illustrated in FIGS. 5, 6, 9,and 10 , the first clutch member 4 a is provided with the inclinedsurfaces 4 aa and 4 ab, and the pressure member 5 is provided withinclined surfaces 5 a and 5 b respectively facing the inclined surfaces4 aa and 4 ab. Specifically, each inclined surface 4 aa comes intoabutment with the associated inclined surface 5 a so as to provide thepressing assist cam, and each inclined surface 4 ab comes into abutmentwith the associated inclined surface 5 b so as to provide the backtorque limiter cam.

Suppose that the rotation speed of the engine E is increased and theresulting rotational force received by the input gear 1 and the clutchhousing 2 is transmittable to the output shaft 3 through the firstclutch member 4 a and the second clutch member 4 b (which means that theweight members 10 are each located at a radially outer position). Inthis case, as illustrated in FIG. 20A, the rotational force is appliedto the pressure member 5 in an a-direction, which exerts a force on thepressure member 5 in a c-direction in FIG. 20A under the action of eachpressing assist cam. The pressure member 5 is thus moved in a directionin which its flange 5 c comes closer to the flange 4 bb of the secondclutch member 4 b (i.e., leftward in FIGS. 2 and 3 ) so as to increasethe pressing force exerted on the driving and driven clutch plates 6 and7.

Suppose that the rotation of the output shaft 3 exceeds the rotationspeed of the input gear 1 and the clutch housing 2, resulting in a backtorque. In this case, as illustrated in FIG. 20B, a rotational force isapplied to the clutch member 4 in a b-direction, which moves thepressure member 5 in a d-direction in FIG. 20B under the action of eachback torque limiter cam so as to release the pressing force exerted onthe driving and driven clutch plates 6 and 7. This makes it possible toprevent a malfunction in the power transmission apparatus K or a powersource (i.e., the engine E) caused by the back torque.

As illustrated in FIGS. 11 to 19 , the centrifugal clutch 9 includes theweight members 10 each movable from a radially inner position (see FIG.18 ) to the radially outer position (see FIG. 19 ) with centrifugalforce produced by rotation of the clutch housing 2. When the weightmembers 10 are each located at the radially outer position, thecentrifugal clutch 9 presses the driving and driven clutch plates 6 and7 against each other so as to enable transmission of the driving forceof the engine E to the wheel (i.e., the driving wheel T). When theweight members 10 are each located at the radially inner position, thecentrifugal clutch 9 releases the pressing force exerted on the drivingand driven clutch plates 6 and 7 so as to cut off transmission of thedriving force of the engine E to the wheel (i.e., the driving wheel T).

Specifically, the centrifugal clutch 9 includes the weight members 10,each of which is a substantially symmetrical polygonal member, a holdingmember 11 (holder) including a supporting member 13 (support) attachedthereto, a pressing member 12 (press), first spherical members 14 (firstspherical bodies), second spherical members 15 (second sphericalbodies), and urging members 16, each of which is a coil spring. Asillustrated in FIGS. 12, 13, and 15 , the holding member 11 and thepressing member 12 are each circumferentially provided on its outerperipheral edge with a plurality of protrusions. The holding member 11is provided with protrusions 11 d, and the pressing member 12 isprovided with protrusions 12 d. The protrusions (11 d, 12 d) are fittedand attached to a fitting portion of the clutch housing 2 through whichthe driving clutch plates 6 are fitted to the clutch housing 2. In thepresent preferred embodiment, the fitting portion is defined by thecut-outs 2 a. Accordingly, similarly to the driving clutch plates 6, theholding member 11 and the pressing member 12 are movable in the axialdirection of the clutch housing 2 and in engagement with the clutchhousing 2 in the direction of rotation so as to be rotatable togetherwith the clutch housing 2.

As illustrated in FIG. 16 , each weight member 10 is a substantiallysymmetrical polygonal member including a first surface X and a secondsurface Y. As illustrated in FIGS. 16 and 17 , each weight member 10includes through holes 10 a passing through the weight member 10 fromthe first surface X to the second surface Y, insertion portions 10 bdefined in the second surface Y, and a groove 10 c defined in the firstsurface X. As illustrated in FIGS. 18 and 19 , the weight members 10 areeach housed in an associated one of housing portions 11 a of the holdingmember 11. When no centrifugal force is applied to the weight members10, the weight members 10 are each held at the radially inner position(see FIG. 18 ). Application of centrifugal force to the weight members10 moves the weight members 10 outward against the urging force of theurging members 16 such that each weight member 10 reaches the radiallyouter position (see FIG. 19 ).

The holding member 11 holds the weight members 10 such that each weightmember 10 is movable between the radially inner position and theradially outer position. As illustrated in FIG. 13 , the holding member11 is an annular member. The holding member 11 includes the housingportions 11 a which are arranged in the circumferential direction of theholding member 11 and in which the weight members 10 are to be housed,groove geometries 11 b defined in the housing portions 11 a, and apushing surface 11 c. Each housing portion 11 a has a recessed shapeconforming to the shape and moving range of the associated weight member10. An inner peripheral wall surface 11 aa of each housing portion 11 ais allowed to abut against first ends of the associated urging members16.

The supporting member 13 is secured to a surface of the holding member11, which is provided with the housing portions 11 a. The supportingmember 13 is able to hold the weight members 10 so as to preventdisconnection of the weight members 10. As illustrated in FIG. 14 , thesupporting member 13 is provided with radially extending holdingportions 13 a. The holding portions 13 a each conform to the groove 10 cof the associated weight member 10, so that the weight members 10 areheld by the holding member 11 while being prevented from beingdisconnected. Specifically, the first surface X of each weight member 10is centrally provided with the groove 10 c extending in a direction fromthe radially inner position to the radially outer position. Causing eachholding portion 13 a to conform to the associated groove 10 c allows theholding member 11 to hold the weight members 10 such that each weightmember 10 is movable in a radial direction (i.e., in a direction fromthe radially inner position to the radially outer position).

In the present preferred embodiment, the holding member 11 having thesupporting member 13 secured thereto as mentioned above defines, asillustrated in FIG. 18 , an integrated assembly N into which the weightmembers 10 (which, in the present preferred embodiment, include theweight members 10, the first spherical members 14, the second sphericalmembers 15, and the urging members 16) that are being held areintegrated. As illustrated in FIGS. 11 and 13 , the holding member 11according to the present preferred embodiment is provided with thepushing surface 11 c located radially inward (or centrally) of thehousing portions 11 a housing the weight members 10.

Specifically, as illustrated in FIGS. 11 and 13 , a first surface F1 ofthe holding member 11 is provided with the housing portions 11 a, and asecond surface F2 of the holding member 11 is provided with the pushingsurface 11 c. The pushing surface 11 c is defined by the bottom of arecess in the second surface F2 (i.e., the bottom of a recess having adepth dimension t as illustrated in the enlarged view of FIG. 11 ). Thisallows the auxiliary clutch plate 17 (which will be described below) tofit within the depth dimension t of the recess and enables the pushingsurface 11 c to push the auxiliary clutch plate 17 when the holdingmember 11 (or the integrated assembly N) and the pressing member 12 moveaway from each other in response to movement of each weight member 10 tothe radially outer position.

Movement of each weight member 10 from the radially inner position tothe radially outer position causes the pressing member 12 to move in astacking direction of the driving and driven clutch plates 6 and 7(i.e., rightward in FIGS. 2 and 3 ) such that the driving and drivenclutch plates 6 and 7 are pressed against each other. Specifically, asillustrated in FIG. 15 , the pressing member 12 is an annular member.The pressing member 12 includes inclined grooves 12 a arranged in thecircumferential direction of the pressing member 12, groove geometries12 b each defined at a position where the associated inclined groove 12a is defined, and a pushing surface 12 c.

Each inclined groove 12 a is defined at a position corresponding to theposition of the associated weight member 10. Each inclined groove 12 ais inclined upward from its inner portion to its outer portion. Thus,when the clutch housing 2 is stationary, each weight member 10 is heldat the radially inner position with the urging force of the associatedurging members 16. Rotation of the clutch housing 2 applies centrifugalforce to the weight members 10 so as to move the weight members 10 alongthe inclined grooves 12 a inclined upward. This moves the pressingmember 12 away from the holding member 11 (i.e., in the direction inwhich the driving and driven clutch plates 6 and 7 are to be pressedagainst each other).

When the holding member 11 and the pressing member 12 are assembled tothe fitting portion (i.e., the cut-outs 2 a) of the clutch housing 2,with the weight members 10 interposed therebetween, each inclined groove12 a is located at a position corresponding to the position of theassociated weight member 10 as illustrated in FIGS. 11 and 12 . Withcentrifugal force, the weight members 10 each move along the inclinedgrooves 12 a from the radially inner position to the radially outerposition, which moves the pressing member 12 in a direction indicated bythe arrow in FIG. 11 (i.e., rightward in FIG. 11 ). The pushing surface12 c of the pressing member 12 thus pushes the driving and driven clutchplates 6 and 7 such that the driving and driven clutch plates 6 and 7are pressed against each other. The resulting reaction force moves theholding member 11 in a direction opposite to the direction indicated bythe arrow in FIG. 11 (i.e., leftward in FIG. 11 ), so that the pushingsurface 11 c of the holding member 11 presses the auxiliary clutch plate17.

As illustrated in FIGS. 18 and 19 , the weight members 10 according tothe present preferred embodiment are each housed in an associated one ofthe housing portions 11 a arranged in the circumferential direction ofthe holding member 11 such that the weight members 10 are movableradially. More than one urging member 16 (i.e., two urging members 16 inthe present preferred embodiment) is disposed in the circumferentialdirection between the inner peripheral wall surface 11 aa (see FIG. 13 )of each of the housing portions 11 a and an associated one of the weightmembers 10 so as to urge the associated weight member 10 from theradially outer position to the radially inner position. In thispreferred embodiment, the inner peripheral wall surface 11 aa of eachhousing portion 11 a is a flat surface in abutment with the first endsof the associated urging members 16 such that the urging members 16 arestably securable.

The weight members 10 according to the present preferred embodiment areeach provided with the tunnel-shaped insertion portions 10 b which areopenings defined in a surface of each weight member 10 facing theholding member 11 (i.e., the second surface Y in FIG. 17 ) and intowhich the urging members 16 are inserted such that the urging members 16are attachable to the associated weight member 10. The weight members10, with the urging members 16 inserted into the insertion portions 10b, are housed in the housing portions 11 a of the holding member 11. Theurging members 16 are thus secured such that each urging member 16 isinterposed between the inner peripheral wall surface 11 aa of theassociated housing portion 11 a and the associated weight member 10. Theurging members 16 are disposed such that the first end of each urgingmember 16 is in abutment with the associated inner peripheral wallsurface 11 aa and a second end of each urging member 16 is in abutmentwith an end wall surface 10 ba of the associated insertion portion 10 b,making it possible to urge each weight member 10 from the radially outerposition to the radially inner position.

Each first spherical member 14 is a steel ball attached to theassociated weight member 10. As illustrated in FIGS. 16 and 17 , eachfirst spherical member 14 is partially protruded from a first opening 10aa (i.e., a small-diameter opening in the first surface X) of thethrough hole 10 a defined in the associated weight member 10 and is incontact with a rolling contact surface of the pressing member 12 so asto be rollable thereon. Each second spherical member 15 is a steel ballattached to the associated weight member 10. As illustrated in FIGS. 16and 17 , each second spherical member 15 is partially protruded from asecond opening 10 ab (i.e., a large-diameter opening in the secondsurface Y) of the through hole 10 a defined in the associated weightmember 10 and is in contact with a rolling contact surface of theholding member 11 so as to be rollable thereon.

As illustrated in FIG. 17 , the through holes 10 a according to thepresent preferred embodiment are tapered such that the diameter of eachthrough hole 10 a continuously increases from the first opening 10 aa(i.e., the small-diameter opening in the first surface X) to the secondopening 10 ab (i.e., the large-diameter opening in the second surfaceY). Disconnection of each first spherical member 14 from the associatedthrough hole 10 a is prevented by the outer peripheral edge of one ofthe first opening 10 aa and the second opening 10 ab that has a smallerdiameter (which is, in the present preferred embodiment, the firstopening 10 aa in the first surface X). The first and second sphericalmembers 14 and 15 according to the present preferred embodiment arespherical members having different diameters in accordance with theinner diameters of the through holes 10 a. The second spherical members15 are larger in diameter than the first spherical members 14. Thesmall-diameter first spherical members 14 are each rollable while beingin contact with the inner peripheral surface of the associated throughhole 10 a, and at the same time, disconnection of the small-diameterfirst spherical members 14 is prevented by the small-diameter openingedges of the through holes 10 a.

As illustrated in FIGS. 11 and 12 , disconnection of the secondspherical members 15 is prevented by the rolling contact surface of theholding member 11. Thus, disconnection of the small-diameter firstspherical members 14 is prevented by the small-diameter opening edges ofthe through holes 10 a, and disconnection of the large-diameter secondspherical members 15 is prevented by the rolling contact surface of theholding member 11 while the second spherical members 15 are partiallyprotruded from the large-diameter openings of the through holes 10 a. Inthe present preferred embodiment, the large-diameter second sphericalmembers 15 are assembled to the weight members 10 such that the secondspherical members 15 face the rolling contact surface of the holdingmember 11. Alternatively, the second spherical members 15 may beassembled to the weight members 10 such that the second sphericalmembers 15 face the rolling contact surface of the pressing member 12.In this case, disconnection of the small-diameter first sphericalmembers 14 is prevented by the small-diameter opening edges of thethrough holes 10 a, and disconnection of the large-diameter secondspherical members 15 is prevented by the rolling contact surface of thepressing member 12 while the second spherical members 15 are partiallyprotruded from the large-diameter openings of the through holes 10 a.

As illustrated in FIG. 13 , the rolling contact surface of the holdingmember 11 (which is, in the present preferred embodiment, a surface ofthe holding member 11 on which the second spherical members 15 roll)includes the groove geometries 11 b each extending in the direction ofmovement of the associated weight member 10 (i.e., a directionconnecting the radially inner position to the radially outer position).As illustrated in FIG. 15 , the rolling contact surface of the pressingmember 12 (which is, in the present preferred embodiment, a surface ofthe pressing member 12 on which the first spherical members 14 roll)includes the groove geometries 12 b each extending in the direction ofmovement of the associated weight member 10 (i.e., a directionconnecting the radially inner position to the radially outer position).

As illustrated in FIGS. 16, 18, and 19 , the first and second sphericalmembers 14 and 15 according to the present preferred embodiment areprovided such that more than one first spherical member 14 and more thanone second spherical member 15 are arranged in the circumferentialdirection of the holding member 11 (i.e., such that two first sphericalmembers 14 and two second spherical members 15 are arranged in the widthdirection of each weight member 10 in the present preferred embodiment).In response to movement of the weight members 10, the first sphericalmembers 14 are movable along the groove geometries 12 b while rollingwithin the through holes 10 a, and the second spherical members 15 aremovable along the groove geometries 11 b while rolling within thethrough holes 10 a.

The auxiliary clutch plate 17 is an annular member different in diameterfrom the driving and driven clutch plates 6 and 7 (i.e., smaller indiameter than the driving and driven clutch plates 6 and 7 in thepresent preferred embodiment). As illustrated in FIGS. 2 and 3 , theoutput shaft 3 (i.e., the output) is inserted through a central opening17 a of the auxiliary clutch plate 17 so as to be fitted thereto. Theauxiliary clutch plate 17 includes a pushed surface 17 b facing thepushing surface 11 c of the holding member 11.

When the weight members 10 are each located at the radially outerposition (i.e., when the driving and driven clutch plates 6 and 7 arepressed against each other), the auxiliary clutch plate 17 is able totransmit the driving force of the engine E to the output shaft 3 uponbeing pushed by the pushing surface 11 c of the holding member 11 andpressed against the pushing surface 11 c. When the weight members 10 areeach located at the radially inner position (i.e., when the pressingforce exerted on the driving and driven clutch plates 6 and 7 isreleased), the auxiliary clutch plate 17 is able to cut off transmissionof the driving force of the engine E to the output shaft 3 upon beingrelieved of a pressing force applied thereto, owing to a decrease inpushing force exerted by the pushing surface 11 c of the holding member11.

Upon movement of each weight member 10 to the radially outer position,each inclined groove 12 a functions as a cam so as to cause the holdingmember 11 and the pressing member 12 to move away from each other.Accordingly, the pushing surface 12 c of the pressing member 12 pressesthe driving and driven clutch plates 6 and 7 against each other, and thepushing surface 11 c of the holding member 11 pushes the pushed surface17 b of the auxiliary clutch plate 17 such that the pushed surface 17 bis pressed against the pushing surface 11 c so as to transmit thedriving force of the engine E to the driving wheel T.

As already described, the holding member 11 according to the presentpreferred embodiment defines the integrated assembly N into which theweight members 10 that are being held are integrated. The integratedassembly N and the pressing member 12 are separate components notconnected to each other through a fastener, such as a bolt, and areindependently movable toward or away from each other. The integratedassembly N and the pressing member 12, which are not connected to eachother, are each attached to the fitting portion (i.e., the cut-outs 2 a)of the clutch housing 2. Accordingly, if the pressing member 12 moveswhile being inclined relative to the axial direction (which correspondsto the direction of a rotation axis of the clutch housing 2) uponasynchronous radial movement of more than one weight member 10, all ofthe weight members 10 would eventually move to the radially outerposition. This corrects the inclination of the pressing member 12,enabling the pressing member 12 to press the driving and driven clutchplates 6 and 7 against each other successfully.

As illustrated in FIGS. 5 and 6 , a portion of a surface of the firstclutch member 4 a according to the present preferred embodiment, whichfaces the pressure member 5, defines an abutment surface 4 ad. Asillustrated in FIGS. 9 and 10 , a portion of a surface of the pressuremember 5, which faces the first clutch member 4 a, defines an abutmentsurface 5 e. With the first clutch member 4 a, the second clutch member4 b, and the pressure member 5 assembled to each other (and with notorque being transmitted from the input gear 1 (i.e., the input) to theoutput shaft 3 (i.e., the output)), the abutment surface 4 ad and theabutment surface 5 e are in abutment with each other as illustrated inFIGS. 2 and 3 .

With the abutment surface 4 ad and the abutment surface 5 e in abutmentwith each other as mentioned above, in the course of movement of eachweight member 10 of the centrifugal clutch 9 from the radially innerposition (see FIG. 22 ) to an intermediate position (see FIG. 23 ) and aresulting increase in torque transmitted from the input gear 1 (i.e.,the input) to the output shaft 3 (i.e., the output), the first clutchmember 4 a and the pressure member 5 are not allowed to move relative toeach other, which restricts operation of the pressing assist cams.

Each weight member 10 of the centrifugal clutch 9 then further movesfrom the intermediate position (see FIG. 23 ) to the radially outerposition (see FIG. 24 ), and the driving and driven clutch plates 6 and7 are pushed by the flange 4 bb of the second clutch member 4 b and thuspressed against each other. When the pushing force of the flange 4 bb isequal to or greater than the urging force of the clutch springs S, thesecond clutch member 4 b and the pressure member 5 are moved in theaxial direction (i.e., rightward in FIGS. 2 and 3 ) relative to thefirst clutch member 4 a, so that the abutment surface 4 ad of the firstclutch member 4 a and the abutment surface 5 e of the pressure member 5are spaced away from each other. FIG. 25 illustrates a state in whichthe weight members 10 are each located at the radially outer positionand the pressure member 5 is located at the non-operating position(i.e., a clutch-disengaged state).

With the abutment surface 4 ad and the abutment surface 5 e spaced awayfrom each other as mentioned above, in the course of movement of eachweight member 10 of the centrifugal clutch 9 from the radially innerposition to the radially outer position and a resulting increase intorque transmitted from the input gear 1 (i.e., the input) to the outputshaft 3 (i.e., the output), the first clutch member 4 a and the pressuremember 5 are allowed to move relative to each other, which allowsoperation of the pressing assist cams.

In the power transmission apparatus K according to the present preferredembodiment, the holding member 11 and the pressing member 12 are eachprovided with more than one protrusion (11 d, 12 d) arrangedcircumferentially. The protrusions (11 d, 12 d) are fitted and attachedto the fitting portion (i.e., the cut-outs 2 a) of the clutch housing 2.The holding member 11 defines the integrated assembly N into which theweight members 10 that are being held are integrated. The integratedassembly N and the pressing member 12 are non-connected separatecomponents and are independently movable toward or away from each other.Accordingly, the present preferred embodiment is able to place thecentrifugal clutch 9 at any location where the fitting portion of theclutch housing 2 is defined, improve workability during assembly of thecentrifugal clutch 9, and successfully move the pressing member 12 inresponse to movement of the weight members 10.

The holding member 11 according to the present preferred embodiment isprovided with the housing portions 11 a housing the weight members 10.The holding member 11 having the supporting member 13 (which is able tohold the weight members 10 so as to prevent disconnection of the weightmembers 10) secured thereto defines the integrated assembly N.Accordingly, the present preferred embodiment is able to reliablyprevent the weight members 10 (which, in the present preferredembodiment, include the weight members 10, the first spherical members14, the second spherical members 15, and the urging members 16) fromfalling off during assembly of the centrifugal clutch 9.

The holding member 11 according to the present preferred embodiment isprovided with the pushing surface 11 c located radially inward of thehousing portions 11 a housing the weight members 10. When the holdingmember 11 (or the integrated assembly N) and the pressing member 12 moveaway from each other in response to movement of each weight member 10 tothe radially outer position, the pushing surface 12 c of the pressingmember 12 is able to press the driving and driven clutch plates 6 and 7against each other, and the pushing surface 11 c of the holding member11 is able to push the auxiliary clutch plate 17 smaller in diameterthan the driving and driven clutch plates 6 and 7. Accordingly, with thecentrifugal clutch 9, the present preferred embodiment is able to pressthe driving and driven clutch plates 6 and 7 against each other and pushthe auxiliary clutch plate 17 simultaneously.

The holding member 11 according to the present preferred embodimentincludes the first surface F1 provided with the housing portions 11 a,and the second surface F2 provided with the pushing surface 11 c. Thepushing surface 11 c is defined by the bottom of the recess in thesecond surface F2. Accordingly, the present preferred embodiment enablesthe auxiliary clutch plate 17 to fit within the depth dimension t of therecess so as to reduce the dimension of the apparatus in the axialdirection (which corresponds to the right-left direction in FIGS. 2 and3 ), resulting in a reduction in the size of the apparatus.

In addition, the through holes 10 a of the weight members 10 included inthe centrifugal clutch 9 according to the present preferred embodimenteach have a tapered shape from the first opening 10 aa to the secondopening 10 ab. Disconnection of each first spherical member 14 isprevented by the outer peripheral edge of one of the associated firstopening 10 aa and the associated second opening 10 ab that has a smallerdiameter. Accordingly, the present preferred embodiment is able toeasily and accurately attach the first spherical members 14 to theweight members 10, resulting in a reduction in manufacturing cost.

The first and second spherical members 14 and 15 are spherical membershaving different diameters in accordance with the inner diameters of thethrough holes 10 a. The first and second spherical members 14 and 15 arerollable while being in contact with the inner peripheral surfaces ofthe through holes 10 a. Thus, during movement of the weight members 10,the first and second spherical members 14 and 15 are rollable in astable manner such that the weight members 10 move smoothly.Disconnection of the second spherical members 15 according to thepresent preferred embodiment is prevented by the rolling contact surfaceof the holding member 11 or the pressing member 12. Accordingly, thepresent preferred embodiment is able to facilitate preventingdisconnection of the first and second spherical members 14 and 15.

The rolling contact surface of the holding member 11 or the pressingmember 12 includes the groove geometries (11 b, 12 b) extending in thedirection of movement of the weight members 10. Accordingly, the presentpreferred embodiment enables smoother movement of the weight members 10while reliably preventing disconnection of the second spherical members15 from the large-diameter openings and disconnection of the firstspherical members 14 from the small-diameter openings.

In addition, the weight members 10 according to the present preferredembodiment are each housed in an associated one of the housing portions11 a arranged in the circumferential direction of the holding member 11and are thus movable radially. More than one urging member 16 isdisposed in the circumferential direction between the inner peripheralwall surface 11 aa of each of the housing portions 11 a and anassociated one of the weight members 10 so as to urge the associatedweight member 10 from the radially outer position to the radially innerposition. Accordingly, the present preferred embodiment is able toaccurately urge each weight member 10 from the radially outer positionto the radially inner position, enabling stable movement of the weightmembers 10 in accordance with centrifugal force.

The weight members 10 according to the present preferred embodiment areeach provided with the insertion portions 10 b which are openingsdefined in the surface of each weight member 10 facing the holdingmember 11 and into which the urging members 16 are inserted such thatthe urging members 16 are attachable to the associated weight member 10.This facilitates assembling the urging members 16 to the weight members10. The weight members 10 according to the present preferred embodimentare each provided with the groove 10 c extending in a direction from theradially inner position to the radially outer position. The holdingmember 11 (or specifically, the supporting member 13 secured to theholding member 11 so as to be integral therewith) is provided with theholding portions 13 a each conforming to the associated groove 10 c andholding the associated weight member 10. Accordingly, the presentpreferred embodiment enables stable movement of the weight members 10.

The centrifugal clutch 9 according to the present preferred embodimentincludes the first spherical members 14 that are partially protrudedfrom the first openings 10 aa of the through holes 10 a defined in theweight members 10 and are in contact with the rolling contact surface(or the groove geometries 12 b) of the pressing member 12 so as to berollable thereon, and the second spherical members 15 that are partiallyprotruded from the second openings 10 ab of the through holes 10 adefined in the weight members 10 and are in contact with the rollingcontact surface (or the groove geometries 11 b) of the holding member 11so as to be rollable thereon. Accordingly, the present preferredembodiment enables more stable movement of the weight members 10.

The holding member 11 or the pressing member 12, in particular, includesthe groove geometries (11 b, 12 b) extending in the direction ofmovement of the weight members 10. The groove geometries (11 b, 12 b)define the rolling contact surface for the first spherical members 14 orthe second spherical members 15 so as to enable smoother movement of theweight members 10. The first and second spherical members 14 and 15according to the present preferred embodiment are provided such thatmore than one first spherical member 14 and more than one secondspherical member 15 are arranged in the circumferential direction of theholding member 11 (i.e., the width direction of each weight member 10).Accordingly, the present preferred embodiment enables more stablemovement of the weight members 10.

Although the present preferred embodiment has been described thus far,the present invention is not limited to this preferred embodiment. Inone example, the apparatus may include no pressing assist cam (whichincludes the inclined surfaces 4 aa and 5 a) or no back torque limitercam (which includes the inclined surfaces 4 ab and 5 b). In anotherexample, the apparatus may include no auxiliary clutch plate 17. In thepresent preferred embodiment, disconnection of the second sphericalmembers 15 is prevented by the rolling contact surface (or the groovegeometries 11 a) of the holding member 11 (or the pressing member 12).Alternatively, disconnection of the second spherical members 15 may beprevented by any other disconnection preventing structures and methods,such as swaging.

In the present preferred embodiment, with the first clutch member 4 a,the second clutch member 4 b, and the pressure member 5 assembled toeach other (and with no torque being transmitted from the input gear 1(i.e., the input) to the output shaft 3 (i.e., the output)), theabutment surface 4 ad and the abutment surface 5 e are in abutment witheach other. Alternatively, the first clutch member 4 a may include noabutment surface 4 ad, the pressure member 5 may include no abutmentsurface 5 e, and the first clutch member 4 a and the pressure member 5may be spaced away from each other. The power transmission apparatusesaccording to preferred embodiments of the present invention may findapplications as various multiple-plate clutch type power transmissionapparatuses for, for example, motorcycles, automobiles, three-wheel orfour-wheel buggies, or general purpose machines.

A power transmission apparatus includes a centrifugal clutch including aholder holding a mass such that the mass is movable between a radiallyinner position and a radially outer position, and a press to pressdriving and driven clutch plates against each other by moving in astacking direction of the driving and driven clutch plates in responseto movement of the mass from the radially inner position to the radiallyouter position. The holder and the press are each provided with aplurality of protrusions arranged circumferentially and fitted andattached to a fitting portion of a clutch housing. The holder defines anintegrated assembly into which the mass that is being held isintegrated. The integrated assembly and the press are non-connectedseparate components and are independently movable toward or away fromeach other. Such a power transmission apparatus may find applicationsinvolving, for example, change(s) in external shape or addition of otherfunction(s).

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

The invention claimed is:
 1. A power transmission apparatus comprising:a clutch housed in a clutch housing that rotates together with an inputthat rotates due to a driving force of an engine of a vehicle, theclutch housing including a fitting portion having a plurality of drivingclutch plates fitted and attached thereto, the clutch having a pluralityof driven clutch plates attached thereto, the driven clutch plates beingalternately arranged with the driving clutch plates, the clutch beingconnected to an output that is able to rotate a wheel of the vehicle; apressure applicator movable between an operating position where thedriving and driven clutch plates are pressed against each other so as toenable transmission of the driving force of the engine to the wheel anda non-operating position where a pressing force exerted on the drivingand driven clutch plates is released so as to cut off transmission ofthe driving force of the engine to the wheel; and a centrifugal clutchincluding a mass movable from a radially inner position to a radiallyouter position due to centrifugal force produced by rotation of theclutch housing, the centrifugal clutch being configured to, when themass is located at the radially outer position, press the driving anddriven clutch plates against each other so as to enable transmission ofthe driving force of the engine to the wheel and configured to, when themass is located at the radially inner position, release the pressingforce exerted on the driving and driven clutch plates so as to cut offtransmission of the driving force of the engine to the wheel; whereinthe centrifugal clutch includes: a holder holding the mass such that themass is movable between the radially inner position and the radiallyouter position; a support secured to the holder and holding the massbetween the support and the holder; and a press independently movabletoward or away from the holder and the support; and the press isoperable to press the driving and driven clutch plates against eachother by moving in a direction toward the driving and driven clutchplates in response to movement of the mass from the radially innerposition to the radially outer position.
 2. The power transmissionapparatus according to claim 1, wherein the holder includes a housingportion housing the mass; and the support is secured to the holder suchthat the support covers the housing portion.
 3. The power transmissionapparatus according to claim 1, wherein the holder is movable in adirection opposite to a direction of movement of the press responsive tomovement of the mass from the radially inner position to the radiallyouter position.
 4. The power transmission apparatus according to claim3, further comprising: an auxiliary clutch plate secured to the output;wherein upon movement of the holder in the direction opposite to thedirection of movement of the press responsive to movement of the massfrom the radially inner position to the radially outer position, theholder presses the auxiliary clutch plate.
 5. The power transmissionapparatus according to claim 4, wherein a surface of the holder locatedon a first side in an axial direction of the output includes a housingportion housing the mass, and a surface of the holder located on asecond side in the axial direction of the output includes a pushingsurface to press the auxiliary clutch plate; and the pushing surface isdefined by a bottom of a recess in the surface of the holder located onthe second side.
 6. The power transmission apparatus according to claim5, wherein the auxiliary clutch plate is housed in the recess.
 7. Thepower transmission apparatus according to claim 4, wherein the clutchhousing includes a disk portion attached to the input; the holder facesthe disk portion; and the holder and the disk portion are spaced awayfrom each other.
 8. The power transmission apparatus according to claim7, wherein the disk portion includes a first flat portion; the holderincludes a second flat portion facing the first flat portion andparallel to the first flat portion; and a space is defined between thefirst flat portion and the second flat portion.
 9. The powertransmission apparatus according to claim 1, wherein the holder ismovable in a direction opposite to a direction of movement of the pressresponsive to movement of the mass from the radially outer position tothe radially inner position.
 10. The power transmission apparatusaccording to claim 1, wherein the press is movable in conjunction withmovement of the mass without involvement of the support.